Optical system and image pickup apparatus

Abstract

An optical system includes first to third units. The first unit includes a first substrate and a first lens having negative refractive power. The first lens is disposed on the image side of the first substrate. The second unit includes a second substrate and a second lens having positive refractive power. The second lens is disposed on the object side or image side of the second substrate. The third unit includes a third substrate and a third lens having positive refractive power. The third lens is disposed on the object side or image side of the third substrate. At least one of the first to third lenses constitutes a cemented lens including a fourth lens. The fourth lens and the lens cemented with the fourth lens in the cemented lens have refractive powers different from each other and Abbe numbers different from each other.

What is claimed is: 
     
       1. An optical system comprising a plurality of units, the plurality of units consisting of, in order from an object side to an image side, a first unit, a second unit, and a third unit,
 wherein the first unit includes a first substrate and a first lens having negative refractive power, the first lens being disposed on the image side of the first substrate, 
 wherein the second unit includes a second substrate and a second lens having positive refractive power, the second lens being disposed on the object side or image side of the second substrate, 
 wherein the third unit includes a third substrate and a third lens having positive refractive power, the third lens being disposed on the object side or image side of the third substrate, 
 wherein at least one of the first lens, the second lens, and the third lens constitutes a cemented lens including a fourth lens, and 
 wherein the fourth lens and the lens cemented with the fourth lens in the cemented lens have refractive powers different from each other and Abbe numbers different from each other. 
 
     
     
       2. The optical system according to  claim 1 , wherein the following inequality is satisfied:
   8<| vr−vb|< 60 
 
       where vr is the Abbe number of the fourth lens, and vb is the Abbe number of the lens cemented with the fourth lens. 
     
     
       3. The optical system according to  claim 1 , wherein the following inequality is satisfied:
   0.05< dsm/f< 2.50 
 
       where dsm is a distance on an optical axis from a cemented surface of the cemented lens to an aperture stop, and f is a focal length of the optical system. 
     
     
       4. The optical system according to  claim 3 , wherein the aperture stop is disposed on the second substrate or the third substrate. 
     
     
       5. The optical system according to  claim 1 , wherein the following inequalities are satisfied:
   0.05<| f 7 r/fr− 1|<20.00 
   0.05<| f 7 b/fb− 1|<20.00 
 
       where f7r is a focal length in an area of 70% of an effective diameter of the fourth lens, fr is a paraxial focal length in a central area of the effective diameter of the fourth lens, f7b is a focal length in an area of 70% of the effective diameter of the lens cemented with the fourth lens, and fb is a paraxial focal length in a central area of the effective diameter of the lens cemented with the fourth lens. 
     
     
       6. The optical system according to  claim 1 , wherein the following inequality is satisfied:
   0.000<| f /( f 7 r×vr )+ f /( f 7 b×vb )|<0.050 
 
       where f7r is a focal length in an area of 70% of an effective diameter of the fourth lens, vr is an Abbe number of the fourth lens, f7b is a focal length in an area of 70% of an effective diameter of the lens cemented with the fourth lens, vb is an Abbe number of the lens cemented with the fourth lens, and f is a focal length of the optical system. 
     
     
       7. The optical system according to  claim 1 , wherein the following inequalities are satisfied:
   0.1<| f 7 sm/f 7 r|< 6.0 
   0.1<| f 7 sm/f 7 b|< 6.0 
 
       where f7sm is a focal length in an area of 70% of an effective diameter of the cemented lens, f7r is a focal length in an area of 70% of an effective diameter of the fourth lens, f7b is an effective diameter in an area of 70% of the lens cemented with the fourth lens. 
     
     
       8. The optical system according to  claim 1 , wherein the following inequality is satisfied:
   0.7< f 2/ f< 5.0 
 
       where f2 is a focal length of the second unit, and f is a focal length of the optical system. 
     
     
       9. The optical system according to  claim 1 , wherein the following inequality is satisfied:
   −4.0< f 3/ f 1<−0.3
 
 
       where f1 is a focal length of the first unit, and f3 is a focal length of the third unit. 
     
     
       10. The optical system according to  claim 1 , wherein the following inequality is satisfied:
   0.3<( f 2− f 1)/ f 3<7.0
 
 
       where f1 is a focal length of the first unit, f2 is a focal length of the second unit, and f3 is a focal length of the third unit. 
     
     
       11. The optical system according to  claim 1 , wherein the following inequality is satisfied:
   0.5< f 3/ f< 4.0 
 
       where f3 is a focal length of the third unit, and f is a focal length of the optical system. 
     
     
       12. The optical system according to  claim 1 , wherein the following inequality is satisfied:
   0.5< L/f< 3.5 
 
       where L is a distance on an optical axis from a surface on the image side of the third lens to an image plane. 
     
     
       13. The optical system according to  claim 1 , wherein the following inequality is satisfied:
   −2.0< da 1× f 1/( f×Yim )<−0.3
 
 
       where da 1  is a distance from a lens surface closest to an image plane of a lens in the first unit to an aperture stop, f1 is a focal length of the first unit, f is a focal length of the optical system, and Yim is a maximum image height. 
     
     
       14. The optical system according to  claim 1 , wherein no lens is formed on one surface of the first substrate. 
     
     
       15. The optical system according to  claim 1 , wherein no lens is formed on one of surface of the second substrate. 
     
     
       16. The optical system according to  claim 1 , wherein no lens is formed on one surface of the third substrate. 
     
     
       17. The optical system according to  claim 1 , wherein materials of the first substrate and the first lens are different from each other. 
     
     
       18. The optical system according to  claim 1 , wherein materials of the second substrate and the second lens are different from each other. 
     
     
       19. The optical system according to  claim 1 , wherein materials of the third substrate and the third lens are different from each other. 
     
     
       20. An image pickup apparatus comprising:
 an optical system; and 
 an image sensor configured to receive an image formed by the optical system, 
 wherein the optical system includes a plurality of units, the plurality of units consisting of, in order from an object side to an image side, a first unit, a second unit, and a third unit, 
 wherein the first unit includes a first substrate and a first lens having negative refractive power, the first lens being disposed on the image side of the first substrate, 
 wherein the second unit includes a second substrate and a second lens having positive refractive power, the second lens being disposed on the object side or image side of the second substrate, 
 wherein the third unit includes a third substrate and a third lens having positive refractive power, the third lens being disposed on the object side or image side of the third substrate, 
 wherein at least one of the first lens, the second lens, and the third lens constitutes a cemented lens including a fourth lens, and 
 wherein the fourth lens and the lens cemented with the fourth lens in the cemented lens have refractive powers different from each other and Abbe numbers different from each other.